Patient monitors that acquire and process electroencephalographic (EEG) signals are commonly used in surgical settings to monitor the patient's state or hypnosis and sedation. The EEG is characterized by amplitudes in the microvolt range and frequencies in the 0-50 Hz frequency band. The use of processed EEG can be impaired by radio frequency electrical noise in the operating room environment. It is common surgical practice for a surgeon to use electrosurgical devices as cutting and coagulating tools. Electrosurgical devices typically use AC voltages in the 500 KHz to 3 MHz frequency range. Typical amplitudes may be 100 to 5000 volts. The application of the electrosurgical scalpel frequently causes electrical arcing, generating wide-band electrical noise. In addition, the electrosurgical waveform may be modulated by switching it on and off at a certain duty cycle. This modulation also generates wide-band electrical noise. Electrical noise arising from electrosurgical devices are easily picked up by other monitoring devices in the operating room. Due to their large amplitude and wide-band frequency characteristics, electrosurgical devices are a major source of operating room electrical interference.